A number of chemical agents are known which are effective in increasing the efficiency of feed utilization by ruminants. Monensin, for instance, has found widespread success in promoting feed efficiency in ruminants such as cattle and sheep. Monensin, and numerous other polyether antibiotics and related compounds, function by altering the mechanism of ruminant feed utilization, which mechanism involves fermentation. Microorganisms in the developed rumen of a ruminant animal degrade carbohydrates (the major nutritive portion of ruminant feeds) to produce pyruvates. Pyruvates are further metabolized by microbiological processes to form acetates, butyrates and propionates. These latter compounds are collectively referred to as volatile fatty acids (VFA's). While acetates, butyrates and propionates all are utilized in the growth mechanism and in energy production, the propionates are more efficiently produced and utilized than either the acetates or the butyrates. Some of the known growth promoters and feed utilization enhancers thus function in ruminants having a developed rumen function by increasing the formation of propionates from carbohydrates, at the expense of acetate and butyrate production.
Raun et al., in J. Ani. Sci., 43, 670 (1976), demonstrate that the effectiveness of monensin on feed efficiency reaches a maximum at a dose level of about 30 grams per ton of feed. A similar maximum in effectiveness at a particular dose level is observed with most other feed efficiency enhancers, including the glycopeptides such as avoparcin, actaplanin and the like. This maximum effectiveness has been considered due to an inability to increase propionate production in the rumen beyond a certain level.
It therefore is surprising that the administration of a combination of feed efficiency enhancing agents selected from a glycopeptide and a polyether to an animal having a developed rumen function causes a greater affect upon feed efficiency (i.e., a greater production of propionate) than effected by either agent when administered alone at an optimal dose level. An object of this invention is to provide a combination of feed efficiency enhancing agents which is surprisingly effective in increasing the efficiency of feed utilization in such animals.